A number of applications require the cooling of electronic devices to low cryogenic temperatures for their proper and efficient operation. For example, highly sensitive infrared sensors carried on spacecraft and used for remote sensing must be cooled to a temperature below about 15 K.
A cryogenic refrigeration system is used to achieve such low temperatures. A number of different types of cryogenic refrigeration systems are available, based upon different thermodynamic cycles. For the space applications of most interest, a cryogenic refrigeration system based upon the Joule-Thomson principle is preferred. Briefly, in a preferred Joule-Thomson cryogenic refrigeration system for achieving very low temperatures, helium or other suitable working gas is compressed, precooled, and expanded through an expansion nozzle. The expansion of the gas cools the gas and may liquefy it. The expanded or liquefied gas absorbs heat from the surroundings, such as the infrared sensor. The expanded or liquefied gas is then contacted to the incoming compressed gas in a heat exchanger to precool the incoming compressed gas, and thereafter expelled or, more typically, recycled back through the compressor, heat exchanger, and expansion nozzle. A properly designed Joule-Thomson refrigeration system cycle can reach temperatures of less than 15 K.
Because the working gas expands through the small expansion nozzle and cools, the gas must be free of condensable contaminants. Condensable contaminants, such as gases other than helium, may condense in the orifice of the expansion nozzle to partially or completely plug it, and thereby render the expansion nozzle and the cryogenic refrigeration system partially or completely inoperable.
The compressor is normally the only part of the cryogenic refrigeration system that has moving parts, and it therefore must be carefully selected to avoid contamination of the working gas. Some types of compressors, such as those used for Joule-Thomson cryogenic refrigeration systems operating at higher temperatures, are simply not candidates for low-temperature Joule-Thomson refrigeration systems, because too much contamination reaches the working gas, such as lubricants in the drive and in-leaked gas. The compressor desirably can achieve the required compression ratio in a single compression stage, because a reduction in mechanical complexity is highly desired in a compressor that is largely inaccessible while in space. This desired feature rules out some compressors.
Various other types of compressors could potentially meet these requirements and are therefore candidates for use in Joule-Thomson cryogenic refrigeration systems. Rotary vane compressors can achieve the required pressure ratios in only two stages, but suffer from a contamination of the working gas and wear problems that limit their lives. Sorption compressors may require multiple stages, and they are inefficient and sensitive to poisoning of the sorbent materials. Other multi-step valved compressors can meet the pressure ratio requirements but are also susceptible to contamination of the working gas which may clog the Joule-Thomson expansion orifice. Compressors used in Stirling cycle cryogenic refrigeration systems potentially could be used, but they produce a pressure wave and do not supply the steady pressure needed on the high-pressure nozzle inlet of the expansion nozzle.
There is a need, as yet not met, for a cryogenic refrigeration system operable at low cryogenic temperatures, such as 15 K or less, wherein the compressor meets the requirements discussed above. It is further desirable to satisfy this need with a single stage of compression. The present invention fulfills this need, and further provides related advantages.